Moire reducing optical substrates with irregular prism structures

ABSTRACT

An optical substrate has a structured surface that enhances brightness and reduces moire effect. The optical substrate has a three-dimensionally varying, structured light output surface that comprises an irregular prismatic structure. The irregular prismatic structure may be viewed as comprising longitudinal prism blocks or rows thereof, arranged laterally defining peaks and valleys. Adjacent peaks, adjacent valleys, and/or adjacent peak and valley may be parallel or non-parallel, in an orderly, semi-orderly, random, or quasi-random manner. The lateral adjacent peaks, adjacent valleys, and/or adjacent peak and valley are not parallel. The adjacent irregular prism blocks may be irregular longitudinal sections having the same length, or random or quasi-random irregular sections having different lengths. The facets of each prism block may be flat, or curved (convexly and/or concavely).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/825,170 filed on Aug. 13 2015, which is a continuation of U.S. patentapplication Ser. No. 14/010,478 filed on Aug. 26, 2013, which is acontinuation of U.S. patent application Ser. No. 12/590,855 filed onNov. 12, 2009, now U.S. Pat. No. 8,517,573, which is a continuation ofU.S. patent application Ser. No. 11/450,145 filed on Jun. 9, 2006, nowU.S. Pat. No. 7,618,164, which claims priority of U.S. provisionalapplication Ser. No. 60/689,650 filed on Jun. 9, 2005. All of theseapplications are incorporated by referenced herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical substrates having a structuredsurface, particularly to optical substrates for brightness enhancement,and more particularly to brightness enhancement substrates for use inflat panel displays having a planar light source.

2. Description of Related Art

Flat panel display technology is commonly used in television displays,computer displays, and handheld electronics (e.g., cellular phones,personal digital assistants (PDAs), etc.). Liquid crystal display (LCD)is a type of flat panel display, which deploys a liquid crystal (LC)module having an array of pixels to render an image. In backlight LCDs,brightness enhancement films use prismatic structures to direct lightalong the viewing axes (i.e., normal to the display), which enhances thebrightness of the light viewed by the user of the display and whichallows the system to use less power to create a desired level of on-axisillumination.

Heretofore, brightness enhancement films were provided with parallelprismatic grooves, lenticular grooves, or pyramids on the light emittingsurface of the films, which change the angle of the film/air interfacefor light rays exiting the films and cause light incident obliquely atthe other surface of the films to be redistributed in a direction morenormal to the exit surface of the films. The brightness enhancementfilms have a light input surface that is smooth, through which lightenters from the backlight module. Heretofore, many applications used twobrightness enhancement film layers rotated relative to each other suchthat the grooves in the respective film layers are at 90 degreesrelative to each other.

An undesirable effect arising from using two brightness enhancementfilms in a flat panel display is the appearance of moire patterns causedby the interference of the two periodic patterns of the prismaticstructures on the surfaces of the two brightness enhancement films. Inthe past, brightness enhancement films have been developed with varioussurface structural configurations in an attempt to avoid moire patternformation. In a flat panel display that incorporates a single layer ofbrightness enhancement film, the periodic patterns causing moiré are thepatterns of the prismatic structure on the film itself and the reflectedimage of such patterns (as reflected by other surfaces in the flat paneldisplay). Further, the structures on the brightness enhancement film andthe pixel array in the LC module could create moiré patterns as well.

For example, U.S. Pat. No. 5,280,371 discloses the use of differentspatial frequencies or pitches of parallel for the two layers ofbrightness enhancement films. Further, it discloses rotating at leastone of the brightness enhancement films with respect to the pixel arrayin the LC module such that the longitudinal structures on the film is atan angle to the pixel array to reduce moire effect. However, due toconventional manufacturing processes for brightness enhancement films,significant trimming is required to obtain a rectangular shapedbrightness enhancement film for use with a rectangular flat paneldisplay, such that the prismatic structures are rotated at an anglerelative to the pixel array in the LC module. This significantlyincreases costs of production.

U.S. Pat. No. 5,919,551 discloses a structured optical film withparallel, variable pitch peaks and/or grooves to reduce the visibilityof moire interference patterns and optical displays incorporating one ormore layers of the film. The pitch variations can be over groups ofadjacent peaks and/or valleys or between adjacent pairs of peaks and/orvalleys. The cross sectional views across the optical film remainconstant along the peaks and valley direction.

U.S. Pat. No. 6,862,141 discloses an optical substrate that features athree-dimensional surface having a correlation length of about 1 cm orless. The optical substrate is defined by a first surface structurefunction modulated by a second surface structure function, the firstsurface structure function producing at least one specular componentfrom a first input beam of light. The peaks of the three-dimensionalstructure lie on the same plane. The optical substrate is suitable foruse in a variety of applications, including brightness enhancement. Thisdisclosure proposes a rather complicated method to derive the surfacestructure for the optical substrate. It is unclear from the disclosurehow the optical substrate can actually be physically implemented.Further, it is doubtful of the level of brightness enhancement that canbe achieved with the disclosed structure, as compared to prism films.

What is needed is a cost effective optical substrate that provides asurface structure that both enhances brightness and reduces moire effectin a single substrate.

SUMMARY OF THE INVENTION

The present invention is directed to an optical substrate that possessesa structured surface that enhances luminance or brightness and reducesmoire effect in a single substrate. In one aspect of the presentinvention, the optical substrate is in the form of a film, sheet, plate,and the like, which may be flexible or rigid, having athree-dimensionally varying, structured light output surface thatcomprises an irregular prism structure, and a non-structured, smooth,planar, light input surface.

In one embodiment of the present invention, the light output surface andthe light input surface are generally parallel to each other in theoverall optical substrate structure (i.e., do not form an overallsubstrate structure that is generally tapered, concave, or convex).

In another embodiment of the present invention, the irregular prismstructure at the light output surface may be viewed as comprisinglongitudinal irregular prism blocks arranged laterally (side-by-side),defining peaks and valleys. A facet of the longitudinal irregular prismblock is defined between each adjacent peak and valley. Thelongitudinally varying prismatic structure has one or more of thefollowing structural characteristics. At least a plurality of theirregular prism blocks have a large end tapering to a small end, or froma large width to a narrow width, or from a large peak height to a smallpeak height. Adjacent peaks, adjacent valleys, and/or adjacent peak andvalley are not parallel within at least a range of lateral prism blocks.The adjacent peaks, adjacent valleys, and/or peak and valley mayalternate from parallel to non-parallel in an orderly, semi-orderly,random, or quasi-random manner. Similarly, the non-parallel peaks,valleys and/or peak and valley may alternate between convergence todivergence in reference to a particular longitudinal direction, in anorderly, semi-orderly, random, or pseudo-random manner. All the peaks donot lie in the same plane, and all the valleys may or may not lie in thesame plane. The sections taken across the peaks and valleys in thelongitudinal direction are not constant. The pitch between adjacentpeaks, adjacent valleys, and/or adjacent peak and valley varieslaterally across the prism blocks in an orderly, semi-orderly, random,or quasi-random manner.

In another embodiment of the present invention, the irregular prismstructure at the light output surface may be viewed as comprisingside-by-side or lateral rows of irregular prism blocks, wherein eachlongitudinal row of irregular prism blocks may be viewed as comprising aplurality of irregular prism blocks connected end to end in a continuousmanner. In one embodiment, the smaller end of one prism block isconnected to the smaller end of another prism block along the same row,and the larger end of one prism block is connected to the larger end ofanother prism block along the same row. The lateral adjacent peaks,adjacent valleys, and/or adjacent peak and valley are not parallel. Thepeak and valley structure across the prism blocks many have furtherstructural characteristics similar to the previous embodiment. Theadjacent irregular prism blocks may be irregular longitudinal sectionshaving the same length, or random or quasi-random irregular sectionshaving different lengths.

In a further embodiment of the present invention, the peaks or valleysof adjacent rows of prism blocks may be parallel, and the irregularprism blocks of one row intersect the irregular prism blocks of anotherrow.

In yet another embodiment of the present invention, one or more facetsof each prism block sections may be substantially flat, or curved(convexly and/or concavely).

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of theinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings. In the following drawings, like referencenumerals designate like or similar parts throughout the drawings.

FIG. 1 schematically illustrates the structure of a LCD having anoptical substrate, in accordance with one embodiment of the presentinvention.

FIG. 2 is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with one embodiment ofthe present invention.

FIG. 3 is a top plan view of the structured light output surface in FIG.2.

FIG. 4 is a schematic perspective view of an irregular prism block thatmay be viewed as a building block for structured light output surface ofthe optical substrate, in accordance with one embodiment of the presentinvention.

FIG. 5 is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with another embodimentof the present invention.

FIG. 6 is a schematic perspective view of a plurality of irregular prismblocks aligned in a row, in accordance with one embodiment of thepresent invention.

FIG. 7 is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with a further embodimentof the present invention.

FIG. 8 is a top plan view of the structured light output surface in FIG.7.

FIG. 9A is a schematic perspective view of a plurality of blocks alignedin a row, including a mix of irregular and regular prism blocks, inaccordance with one embodiment of the present invention.

FIG. 9B is a schematic perspective view of an alternate embodiment ofthe row of prism blocks in FIG. 9A, in which the prism blocks are skewedat an angle in plan view, in accordance with another embodiment of thepresent invention.

FIG. 10 is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with yet anotherembodiment of the present invention.

FIG. 11 is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with still a furtherembodiment of the present invention.

FIG. 12 is a top plan view of the structured light output surface inFIG. 11.

FIG. 13 is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with yet a furtherembodiment of the present invention.

FIG. 14 is a top plan view of the structured light output surface inFIG. 13.

FIG. 15 schematically illustrates top plan view of variousconfigurations of end faces in relation to the peak of the prism block.

FIG. 16 is a schematic view of an electronic device comprising an LCDpanel that incorporates the inventive optical substrate of the presentinvention, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present description is of the best presently contemplated mode ofcarrying out the invention. This invention has been described herein inreference to various embodiments and drawings. This description is madefor the purpose of illustrating the general principles of the inventionand should not be taken in a limiting sense. It will be appreciated bythose skilled in the art that variations and improvements may beaccomplished in view of these teachings without deviating from the scopeand spirit of the invention. The scope of the invention is bestdetermined by reference to the appended claims.

The present invention is directed to an optical substrate that possessesa structured surface that enhances brightness and reduces moire effect.In one aspect of the present invention, the optical substrate is in theform of a film, sheet, plate, and the like, which may be flexible orrigid, having a three-dimensionally varying, structured light outputsurface that comprises an irregular prism structure, and anon-structured, smooth, planar, light input surface. By way ofillustration and not limitation, the present invention will be describedin connection with an optical substrate for use in an LCD having an LCpanel defining a generally rectangular display area in which an image isrendered.

FIG. 1 illustrates an example of a flat panel display. A backlight LCD10, in accordance with one embodiment of the present invention,comprises a liquid crystal (LC) display module 12, a planar light sourcein the form of a backlight module 14, and a number of optical filmsinterposed between the LC module 12 and the backlight module 14. The LCmodule 12 comprises liquid crystals sandwiched between two transparentsubstrates, and control circuitry defining a two-dimensional array ofpixels. The backlight module 14 provides planar light distribution,either of the backlit type in which the light source extends over aplane, or of the edge-lit type as shown in FIG. 1, in which a linearlight source 16 is provided at an edge of a light guide 18. A reflector20 is provided to direct light from the linear light source 16 throughthe edge of the light guide 18 into the light guide 18. The light guideis structured (e.g., with a tapered plate and light reflective and/orscattering surfaces defined on the bottom surface facing away from theLC module 12) to distribute and direct light through the top planarsurface facing towards LC module 12. The optical films may include upperand lower diffuser films 22 and 24 that diffuse light from the planarsurface of the light guide 18. The optical films further includes upperand lower structured surface, optical substrates 26 and 28 in accordancewith the present invention, which redistribute the light passing throughsuch that the distribution of the light exiting the films is directedmore along the normal to the surface of the films. The opticalsubstrates 26 and 28 are often referred in the art as luminance orbrightness enhancement films, light redirecting films, and directionaldiffusing films. The light entering the LC module 12 through such acombination of optical films is uniform spatially over the planar areaof the LC module 12 and has relatively strong normal light intensity.The optical substrates in accordance with the present invention may beused with LCDs to be deployed for displays, for example, fortelevisions, notebook computers, monitors, portable devices such as cellphones, PDAs and the like, to make the displays brighter.

In one embodiment of the present invention, the light output surface andthe light input surface are generally parallel to each other in theoverall optical substrate structure (i.e., do not form an overallsubstrate structure that is generally tapered like a light guide platein a backlight module, or that is concave or convex). Referring to FIG.2, the optical substrate 30 has a light input surface 32 that is planarand smooth, and a light output surface 34 that has an irregularprismatic structure that may be viewed as comprising longitudinalirregular prism blocks arranged in lateral rows (i.e., side-by-side).

For ease of reference, the following orthogonal x, y, z coordinatesystem would be adopted in explaining the various directions. As shownin FIG. 2, the x-axis is in the direction across the peaks and valleys,also referred to as the lateral direction. References to thelongitudinal direction of a prism block would be in reference to thepeak 36 in a top plan view of the prism block 35. The y-axis isorthogonal to the x-axis, in a generally longitudinal direction of theprism blocks 35. The prism blocks 35 being irregular in geometry, they-direction may not necessarily lie in the longitudinal direction oralong the peaks when viewed in plan view (see for example, FIG. 3). Thelight input surface 32 lies in an x-y plane. For a rectangular piece ofthe optical substrate, the x and y-axes would be along the orthogonaledges of the substrate. The z-axis is orthogonal to the x and y-axes.The edge showing the ends of the lateral rows of the prism blocks liesin the x-z plane, such as shown in FIG. 2. References to cross sectionsof a prism block 35 would be sections taken in x-z planes, at variouslocations along the y axis. Further, references to a horizontaldirection would be in an x-y plane, and references to a verticaldirection would be in the z-direction.

FIG. 4 illustrates a single longitudinal, irregular, prism block 35. Theprism block 35 may be viewed as a building block for the opticalsubstrate in accordance with one embodiment of the present invention. Itis noted that, as will be apparent in the discussion herein below, theprism blocks are connected to adjoining prism blocks in longitudinaland/or lateral directions. Because the prism blocks are not in factindividual discrete blocks assembled together, the material of the prismblocks are in a continuum or continuous monolithic structure, with nophysical contact or joining surfaces per se. However, for ease ofillustrating the present invention, the structured surfaces of theoptical substrate may be viewed as being made up of a plurality of prismblocks. Nonetheless, the outline of the faceted structure of the prismblocks would be apparent from the structured surface. The end faces of aprism block or the valleys would be defined by transitions(schematically shown in the figures as lines of transitions) between thelongitudinally adjoining prism blocks. As will be further noted below,the transition between facets within a prism block (e.g., at the peak)and between facets between prism blocks may be radiused or rounded, butsuch transition can nonetheless be determined from the change isorientations of the facets.

Using the end 40 in FIG. 4 as a reference, the cross-section of theprism block 35 in FIG. 4 is generally triangular, with a thin layer ofsubstrate or rectangular base 31 a below a triangle 29 a (i.e., the baseof the triangle extends downward). It is noted that the base 31 a andtriangle 29 a are part of an integral or monolithic structure. The prismblock 35 includes a large end 39 and a small end 40, and a peak 36sloping in a straight line from the large end 39 to the small end 40.The faces at the ends 39 and 40 of the prism blocks are parallel in theembodiment of FIGS. 2 and 3, with the peaks 36 skewed at an angle to theend faces (as viewed from above in a plan view). (For other embodimentsdiscussed below, the end faces of the prism block may be parallel, withthe peak 36 perpendicular to at least one of the ends or skewed at anangle to at least one of the end faces, or the faces may benon-parallel. See FIG. 15 for examples of the geometry of the end facesof an irregular prism, and the peak in relation to the end faces.) Oneach lateral side of the peak 36 is a flat facet 38 of the prism block.The vertex angle of the peak 36, viewed in an x-z sectional plane alongdifferent sections of the entire length of the prism block 35, remainsconstant (e.g., at an angle chosen at between 70 to 110 degrees,preferably at 90 degrees). This will become more apparent when the peakvertex angles are discussed in reference to the optical substrate 30 inFIG. 2, for example. It is noted that the references to vertex anglesherein refer to the angles of the peak 36, as viewed along crosssections in the x-z planes at locations along the y direction, asdefined above. While FIG. 4 shows the base 31 a to be of uniformthickness, it may be non-uniform thickness, as the height of the valleys37 (in the z-direction) may vary along the longitudinal direction aswell as the lateral direction of the respective valleys 37, as furtherexplained below. Hereinafter, references to heights of peaks and valleysare measured in the z-direction with respect to the planar light inputsurface 32. It is noted that in the sectional views in x-z planes, thevertex angle of the peak 36 and the angle at the bottom of the valley 37(hereinafter referred to as the valley vertex angle) may be roundedinstead of a sharp point, due to manufacturing constraints.

Specifically, a plurality of the longitudinal prism blocks 35 arearranged in lateral rows as shown in FIG. 2. The vertex angles of thepeaks 36 may vary as viewed in the sectional plane perpendicular to bothx-y plane and prism longitudinal direction, but remains constant for thex-z sectional views at different y locations along a prism block (see,for example, parallel sections A-A, B-B, C-C, D-D in FIG. 3). The vertexangle of the peaks 36 is determined, directly or indirectly, by theangle of the tool used to machine the peaks 36 for the mold used to formthe peaks, depending on the process used. For example, the tool may besupported by a stage to translate in various degrees of freedom,including the x, y and z directions, thus resulting inthree-dimensionally varying irregular prism blocks of the structuredsurface of the optical substrate 30, which maintain a constant peakvertex angle in x-z planes at various locations along the y direction.More complex support apparatuses may be used to provide additionaldegrees of freedom about the motions in x, y and z directions and therotations of x, y and z axes to result in prism blocks having morecomplex three-dimensional varying structures.

The facets 38 of adjoining prism blocks 35 intersect to define a valley37. The vertex angles of the valleys 37 may or may not vary acrosslaterally adjoining rows. The prism blocks each may be asymmetricalabout x-y, x-z and/or y-z planes within a prism block, or may besymmetrical about some of the planes (e.g., in FIG. 3, the prism block35 c and 35 h are symmetrical about a vertical y-z plane through thepeaks 36 c and 36 h, respectively). The combinations of prism blocks 35may be asymmetrical across the entire plan area of the optical substrate30, or may be symmetrical along some planes (e.g., the left half sectionof the optical substrate 30 shown in FIG. 3 is symmetrical to the righthalf section about a y-z plane through the valley 37 e between prismblocks 35 e and 35 f). It is noted that the geometries (e.g., overallsize, angle of the large and small ends to the peak 36, heights of peaksand valleys, etc.) may be different for different prism blocks 35 in theoptical substrate 30.

As shown in FIG. 2, the irregular prism structured light output surface34 comprises longitudinal irregular prism blocks 35 a to 35 j, arrangedin lateral rows (i.e., side-by-side), defining peaks 36 a to 36 j andvalleys 37 a to 37 i. As more clearly shown in the top plan view of theoptical substrate 30 illustrated in FIG. 3, the longitudinally varyingprismatic structure has the following structural characteristics inaddition to those already noted above. At least a plurality of theirregular prism blocks each has a large end 39 (having a larger widthand peak height) tapering to a small end 40 (having a smaller width andpeak height). See, for example, prism blocks 35 a, 35 b, 35 d, 35 e, 35f, 35 g, 35 i and 35 j. Referring to FIG. 2, at least some of the peaks36 do not lie in the same horizontal x-y plane within the opticalsubstrate 30, and at least some of the valleys 37 a to 37 i lie in thesame x-y plane within the optical substrate 30 (i.e., the height of thevalleys, or the thickness of the base material between the valleys 37 ato 37 i and the light input surface 32 is constant for some of thevalleys). Alternatively, not shown, at least some of the valleys 37 a to37 i do not lie in the same x-y plane. Further, the height of the valley37 (i.e., the thickness between the valley and the light input surface32) may vary along a valley 37. Further, along opposing edges of theoptical substrate 30 in the x-direction, at least within a range oflaterally arranged irregular prism blocks, the large ends 39 are mixedwith small ends 40 in a random, quasi-random, orderly or semi-orderlyfashion (e.g., alternating between larger widths to narrower widths, orfrom larger peak heights to smaller peak heights). The transitionsbetween laterally adjoining prism blocks (i.e., the valleys 37) arecontinuous (i.e., no steps), even though the transitions are betweenflat facets 38. Alternatively, the transitions between laterallyadjoining prism blocks may be smoothened or rounded, by providing aradius (not shown) at the transitions or connecting points betweenadjoining prism blocks. Such radius in the rounding may result frommanufacturing constraints, but the bulk of the structured surfacefeatures have well defined flat facet faces, except perhaps at thetransition points between adjoining prism blocks and/or along the peaks.

The pitch between adjacent peaks 36, adjacent valleys 37, and/oradjacent peak 36 and valley 37 vary in an orderly, semi-orderly, random,or quasi-random manner. It is noted that an array, pattern orconfiguration of a group of random irregular prism blocks may repeatover a range of area or length over the overall structured light outputsurface of the optical substrate 30, resulting in an overall orderly,semi-orderly or quasi-random pattern or arrangement for the overalloptical substrate, as illustrated in FIG. 10, and discussed below.Adjacent peaks, adjacent valleys, and/or adjacent peak and valley arenot parallel within at least a range of lateral prism blocks. Theadjacent peaks 36, adjacent valleys 37, and/or adjacent peak 36 andvalley 37 may alternate from parallel to non-parallel, in an orderly,semi-orderly, random, or quasi-random manner. Similarly, adjacentnon-parallel peaks 36, adjacent valleys 37 and/or adjacent peak 36 andvalley 37, may alternate between convergence to divergence (in referenceto the same general longitudinal direction of the prism blocks), in anorderly, semi-orderly, random, or pseudo-random manner. The large ends39, and/or the small ends 40, may be the same size and shape, but may bedifferent without departing from the scope and spirit of the presentinvention. Sections of the optical substrate 30 taken across the peaks36 and valleys 37 in an x-z plane at various locations along they-direction and/or in a general longitudinal direction of a particularpeak or valley are not constant. In the embodiment illustrated in FIGS.2 and 3, there are several longitudinal prism blocks 35 c and 35 h thatmay be of uniform width, ends and or peaks and valleys along theirlongitudinal direction. Even though these particular individual prismblocks have regular geometries, they nonetheless contribute to theirregularity of the structured surface taken as a whole, with referenceto other prism blocks.

In another embodiment of the present invention, the irregular prismstructure at the light output surface may be viewed as comprisingside-by-side or lateral rows of irregular prismatic structures, whereineach longitudinal row of irregular prismatic structure may be viewed ascomprising a plurality of irregular prism blocks that intersect or areconnected end to end in a continuous manner. In one embodimentillustrated in FIG. 5, at the light output surface 43, the smaller endof one prism block is connected to the smaller end of another prismblock along the same row, and the larger end of one prism block isconnected to the larger end of another prism block along the same rowwithin the optical substrate 31. FIG. 6 illustrates two longitudinalprism blocks 35 m and 35 n, each similar to the prism block 35 in FIG.4, which are connected end-to-end at the small ends of both prismblocks. The surfaces at both ends of one or more of the longitudinalprism blocks may be parallel, with the peaks perpendicular to the endfaces or skewed laterally at an angle to the end surfaces, as viewedfrom the top of the structured surface of the film 31, or the endsurfaces may be non-parallel. (It is noted that the end faces of theprism blocks may or may not lie in an x-z plane in reference to theoptical substrate 31 in FIG. 5.) FIG. 15 shows top views of examples ofvarious irregular prisms, in particular the relation of the end faces 39and 40 to the peak 36 and the longitudinally tapering sides of therespective prisms. Specifically, the prism block 35 in A has parallelend faces 39 and 40, and the peak 36 is perpendicular to both the endfaces; the prism block 35 in B has non-parallel end faces 39 and 40, andthe peak 36 is perpendicular to the end face 39 only; the prism block 35in C has non-parallel end faces 39 and 40, and the peak 36 is notperpendicular to any end face; and the prism block 35 in D has parallelend faces 39 and 40, and the peak 36 is not perpendicular to any endface.

The longitudinal prism blocks may also be intersected or connectedend-to-end at their large ends, as can be seen in FIG. 5 (e.g., 35 p and35 q). The transitions 27 between longitudinally adjoining prism blocksmay be smoothened or rounded, by providing a radius (not shown) at thetransitions or connecting points between adjoining prism blocks. Theirregular prism blocks 35 in a particular row may have different orsimilar size and geometry (e.g., different lengths, angles of taper, endsurface sizes, etc). For example, instead of alternating betweenirregular prism blocks of generally similar lengths in a row as shown inFIG. 5, irregular prism blocks of different geometries and sizes may beconnected in a row in a orderly, semi-orderly, random or quasi-randommix, to form the structured light output surface 45 illustrated in FIGS.7 and 8 (as will be discussed below, the film 41 shown in FIGS. 7 and 8may include also regular prism blocks in a further embodiment). Forexample, one end of a first irregular prism block 35 r may be connectedto one end of a second irregular prism block 35 s of a different length.A plurality of the rows of irregular prism blocks are arrangedside-by-side or laterally, to form the optical substrate 41.

The transitions 27 between longitudinally adjoining prism blocks in arow and the transitions between rows (i.e., valleys 37) are continuouswith no steps between adjoining prism blocks, even though suchtransitions are between flat facet surfaces (both in a row and betweenrows). The transitions of the straight peaks of the longitudinallyadjoining prism blocks in the same row are also continuous without anystep. Such transitions may be smoothened or rounded by providing acurvature at the transitions, but the bulk of the structured surfaces ofthe prism blocks would be flat facets. In other words, the transitionsare rounded to some extent. The curvature of such rounding may be theresult of manufacturing constraints depending on the use a particulartool and the movement of such tool across the substrate to form thestructured surface. Generally, the length of the curvature section(viewed in the plane in which the curvature lies) is significantlysmaller when compared to the characteristic dimension (length and/orwidth) of the flat facets of the prism blocks (e.g., for purpose ofillustrating the relative extent of the rounding to the facets, thecurvature may be on the order of less than 15%, preferably less than10%, and more preferably less than 5% of the characteristic dimension ofthe flat facet section.)

FIG. 9A shows an alternate embodiment of the intersection or connectionof prism blocks in a row. The row of prism blocks includes longitudinalirregular prism blocks 35 (similar to FIG. 4), and regular prism blocks33 of various sizes (e.g., irregular prism blocks 35 t and 35 u, andregular prism block 33 a and 33 b), depending on the size of theadjoining ends of the irregular prism blocks 35. FIG. 9A shows anexample of two irregular prism blocks 35 and regular prism blocks 33arranged in a row. More prism blocks 33 and 35 may be provided in therow. The irregular prism blocks 35 and the regular prism blocks 33 in aparticular row respectively may have different sizes and/or geometries,or similar size and/or geometry (e.g., different lengths of theirregular prism blocks 35 and/or regular prism blocks 33, angles oftaper of the irregular prism blocks 35, end surface sizes of theirregular prism blocks 35 and regular prism blocks 33, etc.). Further,instead of alternating between a regular prism block 33 and an irregularprism block 35 in a row, regular prism blocks 33 and irregular prismblocks may be connected in a row in any or random mix. For example, oneend of a first irregular prism block 35 may be connected to one end of asecond irregular prism block 35, and the other end of the first prismblock may be connected to a regular prism block 33. The surfaces at bothends of one or more of the prism blocks in FIG. 9A may be parallel, withthe peaks 36 of the prism blocks perpendicular to the end surfaces orskewed laterally at an angle to the end surfaces, or the end surfacesare non-parallel, as viewed from the top. The transitions 27 arecontinuous, and may be smoothened or rounded with a curvature, as notedin the earlier embodiment.

FIG. 9B shows an alternate embodiment of FIG. 9A, in which irregularprism blocks 35 w and 35 x are intersected with or connected to regularprism blocks 33 c and 33 d in an end-to-end fashion, such that the peaksof the prism blocks are skewed at an angle to each other as viewed fromthe top (e.g., 0. to 45 degrees. In this embodiment, either the endfaces of each or both of the irregular prism blocks 35 w and 35 x arenot parallel, and/or the end faces of each or both of the regular prismblocks 33 c and 33 d are not parallel, or in the alternative if the endsurfaces are parallel, the peaks of the prism blocks are notperpendicular to its end surface. As in the earlier embodiments, thetransitions 27 are continuous, and may be smoothened with a curvature.

A plurality of the rows of irregular and regular prism blocks may bearranged side-by-side or laterally, to form the structured light outputsurface of an optical substrate. The film 41 shown in FIGS. 7 and 8 mayinclude a mix of irregular and regular prism blocks (i.e., a combinationof the building blocks shown in FIG. 6, FIGS. 9A and/or 9B).

The peak and valley structure across the prism blocks in the embodimentsof FIG. 7 may have structural characteristics similar to that describedearlier with respect to the embodiment of FIG. 2. For example, the topplan view of the peaks and valleys of the prism blocks are not parallel(i.e., in a lateral direction) over a range of laterally and/orlongitudinally adjoining prism blocks. However in contrast to theembodiment of FIG. 2, in the embodiments of FIG. 7, most of the valleysdo not lie in the same horizontal plane within the film, as the facetsof the prism blocks of one row intersect the facets of the prism blocksof another row, with the lines of intersection of the facets (i.e., thevalleys) at different heights from the light input surface 32, dependingin part on the width of the prism blocks.

FIG. 10 illustrates an embodiment of structured light output surface 46for an optical substrate 49, in which it is more clearly illustratedthat the array of random structured surface features repeats after acertain length or area across the plane of the overall film, thusforming an overall orderly, semi-orderly, or quasi-random irregularprism block structure across the entire structured surface of theoptical substrate 49. The characteristic dimension of the repeated arrayis on the order of every 2 rows to 50 rows, preferably every 2 rows to35 rows, more preferably every 2 rows to 20 rows, or even morepreferably every 2 rows to 10 rows.

In a further embodiment of the present invention, the peaks of adjacentrows of prism blocks are parallel in the lateral direction in the planeof the optical substrate 47 (i.e., in the top view), as illustrated inFIGS. 11 and 12. The structured light output surface 48 of the opticalsubstrate 47 may be viewed as comprising the block structures shown inFIGS. 6 and 9, but in contrast to the earlier embodiment of FIG. 7, thepeaks 36 of the prism blocks in a row is aligned in a straight line, andthe adjacent peaks 36 between adjoining rows are parallel in the planeof the film 47, at least over a range of lateral rows. The surfaces atboth ends of each prism block are parallel with the peak of the prismblock perpendicular to the end surfaces. Similar to the embodiment ofFIG. 7, most of the valleys the present embodiment of FIG. 11 do not liein the same horizontal plane within the film 47, as the facets of theprism blocks of one row intersect the facets of the prism blocks ofanother row, with the lines of intersection (i.e., the valleys) atdifferent heights from the light input surface 32, depending in part onthe width of the prism blocks.

It is noted that in the embodiment of FIGS. 7 and 8 and FIGS. 11 and 12,one prism block 35 intersect another prism block in both thelongitudinal and lateral directions. Further, referring to the left sideof the optical substrate 47 in FIG. 12, a prism block 53 intersect withadjoining prism blocks in a manner such that it terminates in thelongitudinal direction. In this particular example, the peak of theprism block 53 terminates, and the valleys on either side of the prismblock 53 meet to run into a single valley in the longitudinal direction.Still further, referring to FIG. 11, adjoining prism blocks mayintersect in a manner without a transition at some of the adjoiningfacets. For example, referring to FIGS. 11 and 12, at the left corner ofthe optical substrate 47, the facet 61 of one prism block may continueto the facet 63 of an adjoining prism block without any transition.

In yet another embodiment of the present invention, one or more facets50 and/or peaks 55 of one or more prism blocks may be substantiallycurved (convex and/or concave), as shown in the structured surface 54 inFIGS. 13 and 14. The peaks 55 may follow wavy lines, and the facets 50may or may not have wavy surfaces, including both concave and convexsurfaces. The vertex angle of the peak 55 of a wavy prism block may ormay not have a constant angle at x-z plane sectional views along they-direction. It is noted that on either side of a peak 55, other thanmaking both facets curved, one facet may be curved and the other facetmay be flat. Different peaks 55 follow different curves, which mayinclude a section of only one curvature, or many sections havingdifferent curvatures in a random, quasi-random, orderly or semi-orderlymanner along a particular peak. As is clear from FIGS. 13 and 14,adjoining prism blocks across the structured surface 54 may havedifferent curved or wavy peaks and/or facet surfaces, having curvaturesdiffering in a random, quasi-random, orderly or semi-orderly manner.

These additional embodiments may share further features andcharacteristics of the structured surfaces that are similar to theearlier described embodiments.

In accordance with the present invention, the optical substratecomprising an irregular, prismatic, structured light output surface,which enhances brightness and reduces moire patterns, when applied in anLCD for example. While various embodiments of structured light outputsurfaces have been described above independently, it can be appreciatedthat the various embodiments may be combined in a single opticalsubstrate, without departing from the scope and spirit of the presentinvention.

As an example to illustrate the relative dimensions of an opticalsubstrate in accordance with the present invention, the peak height atdifferent x-y locations may vary from as small as on the order of 1 to10 μm, to as large as on the order of 100 to 200 μm. The relative peakheight difference (along a particular peak and/or between lateral peaks)may vary on the order of 1 to 100 μm, the relative height differencebetween valleys may also vary on the order of 1 to 100 μm, the relativewidth difference between peaks may vary on the order of 2 to 200 μm. Thelength of the prism block may vary on the order of 100 μm to 500 mm. Theforegoing dimensions are intended to illustrate the fact that thestructured surface features are microstructures, in the μm range. By wayof example, the overall size of the area of the optical substrate mayvary on the order of 2 mm to 10 m in width and length (and even largerdimensions possible), depending on the particular application (e.g., ina flat panel display of a cellular phone, or in a significantly largerflat panel display of a TV monitor). The characteristic size of theprism blocks on the structured surface of the optical substrate need notchange appreciably with different overall optical substrate size. Theoptical substrates discussed in connection with the various embodimentsdiscuss above may be supported by a base substrate, such as basesubstrate 51 shown in FIG. 2. The optical substrates may be formed withan optically transparent material. The base substrate 51, which may bemade from the same transparent material as the optical substrate 30,provides additional structural support to the relatively thin opticalsubstrate 30, for example. The optical substrate 30 may be flexibleenough to be manufactured in a roll, which is laid on and bonded to theseparate base substrate 51. Alternatively, the base substrate 51 may bean integral part of the monolithic structure of the optical substrate30. The thickness of the base substrate may be on the order of 25 to 300μm thick. The thickness of the base substrate may be thinner or thickerthan this range, depending on the particular application. Generally,though not required, larger size optical substrate may have a thickerbase substrate to provide better support, and a smaller size opticalsubstrate may require a thinner base substrate for smaller scaleapplications.

The structured surface of optical substrate of the present invention maybe generated in accordance with a number of process techniques,including micromachining using hard tools to form molds or the like forthe irregular prismatic profile described above. The hard tools may bevery small diamond tools mounted on CNC (Computer Numeric Control)machines (e.g. turning, milling and ruling/shaping machines). Preferablythese machines may add some vibration devices to assist the tools movingwith small shifts and making prisms with different level ofirregularity. Known STS (Slow Tool Server), FTS (Fast Tool Server) andsome ultrasonic vibration apparatus are examples of the devices. U.S.Pat. No. 6,581,286, for instance, discloses one of the applications ofthe FTS for making grooves on an optical film by using thread cuttingmethod. The tool is mounted onto the machine, to create constant peakvertex angle in relation to x-z planes along the y direction within aprism. By using the devices to form surfaces in the mold in relation toincreasing degrees of freedom, three-dimensionally varying irregularprism blocks of the structured surfaces of the optical substratesdisclosed above can be obtained.

The master may be used to mold the optical substrate directly or used inelectroforming a duplicate of the master, which duplicate is used tomold the optical substrate. The mold may be in the form of a belt, adrum, a plate, or a cavity. The mold may be used to form the prismaticstructure on a substrate through hot embossing of the substrate, and/orthrough the addition of an ultraviolet curing or thermal settingmaterials in which the structures are formed. The mold may be used toform the optical substrate through injection molding. The substrate orcoating material may be any organic, inorganic or hybrid opticallytransparent material and may include suspended diffusion, birefringentor index of refraction modifying particles.

An LCD incorporating the inventive optical substrate in accordance withthe present invention may be deployed in an electronic device. As shownin FIG. 16, an electronic 110 (which may be one of a PDA, mobile phone,television, display monitor, portable computer, refrigerator, etc.)comprises the inventive LCD 10 (FIG. 1) in accordance with oneembodiment of the present invention. The LCD 10 comprises the inventiveoptical substrate described above. The electronic device 110 may furtherinclude within a suitable housing, a user input interface such as keysand buttons (schematically represented by the block 116), image datacontrol electronics, such as a controller (schematically represented byblock 112) for managing image data flow to the LCD panel 10, electronicsspecific to the electronic device 110, which may include a processor,A/D converters, memory devices, data storage devices, etc.(schematically collectively represented by block 118), and a powersource such as a power supply, battery or jack for external power source(schematically represented by block 114), which components are wellknown in the art.

While particular embodiments of the invention have been described hereinfor the purpose of illustrating the invention and not for the purpose oflimiting the same, it will be appreciated by those of ordinary skill inthe art that numerous variations of the details, materials, andarrangements of parts may be made without departing from the scope ofthe invention as defined in the appended claims.

What is claimed is:
 1. A light directing film comprising a firststructured major surface, a second major surface opposite to the firststructured major surface and a reference horizontal plane between thefirst structured major surface and the second major surface, wherein thereference horizontal plane is substantially perpendicular to thethickness direction of the light directing film, wherein the firststructured major surface comprises a plurality of prisms each of whichhas a pair of faces intersecting to form a ridge extending substantiallyalong a first direction, and the plurality of prisms are disposed alonga second direction substantially perpendicular to the first direction,wherein the plurality of prisms comprises a first prism having aconstant vertex angle throughout the entire first prism, wherein theridge of the first prism comprises a first portion and a second portion,wherein the first portion has a constant height relative to thereference horizontal plane, and the second portion has a non-constantheight relative to the reference horizontal plane and a maximum heightrelative to the reference horizontal plane, wherein the maximum heightis larger than the constant height.
 2. The light directing filmaccording to claim 1, wherein the second major surface defines the lightinput surface of the light directing film and the first structured majorsurface defines the light output surface of the light directing film. 3.The light directing film according to claim 1, wherein the height ofeach point on the entire second portion is not smaller than the constantheight of the first portion.
 4. The light directing film according toclaim 1, wherein each of the plurality of prisms extends continuouslyalong the first direction.
 5. The light directing film according toclaim 1, wherein the second portion is different from and adjacent tothe first portion.
 6. The light directing film according to claim 1,wherein each of the plurality of prisms extends continuously andlinearly along the first direction.
 7. The light directing filmaccording to claim 1, wherein the ridge of each of the plurality ofprisms comprises a first portion and a second portion, wherein thesecond portion is different from and adjacent to the first portion.
 8. Alight directing film comprising a first structured major surface, asecond major surface opposite to the first structured major surface anda reference horizontal plane between the first structured major surfaceand the second major surface, wherein the second major surface definesthe light input surface of the light directing film and the firststructured major surface defines the light output surface of the lightdirecting film, and the reference horizontal plane is substantiallyperpendicular to the thickness direction of the light directing film,wherein the first structured major surface comprises a plurality ofprisms each of which has a pair of faces intersecting to form a ridgeextending substantially along a first direction, each of the pluralityof prisms extends continuously along the first direction, and theplurality of prisms are disposed along a second direction substantiallyperpendicular to the first direction, wherein the plurality of prismscomprises a first prism having a constant vertex angle throughout theentire first prism, wherein the ridge of the first prism comprises afirst portion and a second portion, wherein the second portion isdifferent from and adjacent to the first portion, wherein the firstportion has a constant height relative to the reference horizontalplane, and the second portion has a non-constant height relative to thereference horizontal plane and a maximum height relative to thereference horizontal plane, wherein the maximum height is larger thanthe constant height, and the height of each point on the entire secondportion is not smaller than the constant height of the first portion. 9.The light directing film according to claim 8, wherein each of theplurality of prisms is a triangular prism and extends continuously froma first edge of the light directing film to a second edge of the lightdirecting film opposite to the first edge of the light directing film.10. The light directing film according to claim 9, wherein each of theplurality of prisms extends continuously and linearly from a first edgeof the light directing film to a second edge of the light directing filmopposite to the first edge of the light directing film.
 11. The lightdirecting film according to claim 8, wherein the ridge of each of theplurality of prisms comprises a first portion and a second portion,wherein the second portion is different from and adjacent to the firstportion.
 12. A light directing film comprising a first structured majorsurface, a second major surface opposite to the first structured majorsurface and a reference horizontal plane between the first structuredmajor surface and the second major surface, wherein the referencehorizontal plane is substantially perpendicular to the thicknessdirection of the light directing film, wherein the first structuredmajor surface comprises a plurality of prisms each of which has a pairof faces intersecting to form a ridge extending substantially along afirst direction, and the plurality of prisms are disposed along a seconddirection substantially perpendicular to the first direction, whereinthe plurality of prisms comprises a first prism, wherein eachcross-sectional shape of the entire first prism is a triangle, whereinthe ridge of the first prism comprises a first portion and a secondportion, wherein the first portion has a constant height relative to thereference horizontal plane, and the second portion has a non-constantheight relative to the reference horizontal plane and a maximum heightrelative to the reference horizontal plane, wherein the maximum heightis larger than the constant height.
 13. The light directing filmaccording to claim 12, wherein the second major surface defines thelight input surface of the light directing film and the first structuredmajor surface defines the light output surface of the light directingfilm.
 14. The light directing film according to claim 12, wherein theheight of each point on the entire second portion is not smaller thanthe constant height of the first portion.
 15. The light directing filmaccording to claim 12, wherein each of the plurality of prisms extendscontinuously along the first direction.
 16. The light directing filmaccording to claim 12, wherein the second portion is different from andadjacent to the first portion.
 17. The light directing film according toclaim 12, wherein each triangle has the same vertex angle.
 18. The lightdirecting film according to claim 12, wherein each of the plurality ofprisms extends continuously and linearly along the first direction. 19.The light directing film according to claim 12, wherein the second majorsurface defines the light input surface of the light directing film andthe first structured major surface defines the light output surface ofthe light directing film, wherein each of the plurality of prismsextends continuously from a first edge of the light directing film to asecond edge of the light directing film opposite to the first edge ofthe light directing film, wherein the second portion is different fromand adjacent to the first portion, wherein the height of each point onthe entire second portion is not smaller than the constant height of thefirst portion, wherein each triangle has the same vertex angle.
 20. Thelight directing film according to claim 12, wherein the ridge of each ofthe plurality of prisms comprises a first portion and a second portion,wherein the second portion is different from and adjacent to the firstportion.